The automobile has been a very important transportation vehicle for mankind. However, traffic accidents happen too frequently, the reason for which may be the breakdown of the braking system as well as the negligence of men. Since a braking system is installed underneath an automobile, there has not been any simple, fast and reliable manner to detect whether the brake lining is workable except by periodic inspections. Furthermore, since one's driving mannerisms may be different from that of others, prevention of accidents by means of periodic inspections may not be completely effective. The invention herein provides an effective way to resolve the above problem.